1. Field of the Invention
The present invention relates to an illuminating optical system for splitting white light into red, green, and blue colors and to a color image projecting device for projecting a color image onto a screen, for example, using each color of light from the illuminating optical system.
2. The Prior Art
Color image projecting devices are generally known which split white light into colors, transmit each of the colors of light through picture elements, and then integrate the colors of light into one in order to project it onto a screen and so forth. FIG. 2 shows one example of a prior art color image projecting device as including a light source 2, an illuminating optical system 3, and a projection optical system 4.
The light source 2 comprises a lamp 5 that emits the white light, two integrators 6 and 7, a PS conversion element 8 provided between the integrators 6 and 7. White light that is polarized to P polarized light and S polarized light is output from the light source 2.
The illuminating optical system 3 comprises a total reflection mirror 11, a first dichroic mirror 12, a second dichroic mirror 13, a third dichroic mirror 14, and relay lenses 15, 16, and 17. Each of mirrors and lenses is precisely positioned in an optical path. The total reflection mirror 11 totally reflects the white light from the light source 2 toward the first dichroic mirror 12. The first dichroic mirror 12 transmits only the red color of light while reflecting the remaining green and blue colors of light. The second dichroic mirror 13 transmits only the blue color of light reflected off the first dichroic mirror 12 while reflecting the remaining green color of light. The third dichroic mirror 14 reflects the red color of light transmitted through the first dichroic mirror 12. Each relay lens 15, 16, and 17 adjusts a respective optical path of each of the red, green, and blue colors of light separated by each dichroic mirror 13 and 14, whereby the light paths are incident, respectively, on each of a red block 18, a green block 19, and a blue block 20 as described below.
The projection optical system 4 comprises the red block 18, the green block 19, the blue block 20, a condensing block 21, and a projection lens 22. The red block 18 forms a red projection image with the red color light separated by the illuminating optical system 3, the green block 19 forms a green projection image with the green color light separated by the illuminating optical system 3, and the blue block 20 forms a blue projection image with the blue color light separated by the illuminating optical system 3. The condensing block 21 integrates the projection images formed by the red block 18, the green block 19, and the blue block 20 into one projection image. The projection lens 22 projects the projection image integrated by the condensing block 21, onto the screen.
However, in the color image projecting device 1 described above, each mirror 11, 12, 13, and 14 and each lens 15, 16, and 17 is a discrete component and together represent a large number of components. Furthermore, the positioning of these components precisely on the optical path requires a large number of complex assembly steps, resulting in problems such as increased production cost.